Nitrile ylides also known as nitrilium ylides or nitrilium methylides, are generally reactive intermediates[1] formally consisting of a carbanion of an alkyl or similar group bonded to the nitrogen atom of a cyanide unit.
However, a structure has been determined on a particularly stable nitrile ylide by X-ray crystallography.
As resonance structures 1c and 1d become more important the nitrilium ylide distorts its geometry from linear in favor of a different valence tautomer 2 that is distinctly bent: Nitrile ylides are isoelectronic with nitrile oxides:
The synthetically most useful reaction of the nitrile ylides is the 1,3-dipolar cycloaddition to dipolarophiles: with electron-deficient alkenes, good yields of pyrrolines are obtained.
Nitrile ylides react with weak acids like methanol by protonation finally leading to a methoxyimine.